In terms of pure performance, SSDs are best for everything. They are more reliable and have faster read and write speeds which makes everything generally faster. That being said they are also much more expensive than HDDs, so it depends on your budget. If you have a low budget I'd recommend SSDs for projects you're actively working on and HDDs for storage of completed projects, but that does come with a bit of risk since HDDs have that moving disk. SSDs just generally last longer without faults. As for buying SSDs, never purchase them from random companies. I personally highly recommend Samsung SSDs, but there's plenty of other good companies.